Critical dimension (CD) variation is an important metric in the fabrication of integrated chips. Critical dimension variation is a measure of the variation in size of a feature formed on an integrated chip, due to machine variations and/or process variations. For example, a metal line having a critical dimension variation of 5 nm will statistically have 3-σ variation in size of +/−5 nm.
CD variations provide a statistically reliable mechanism for accurate prediction of such things as device performance, reliability, RC extraction, etc. Therefore, the semiconductor industry has dedicated significant effort to control critical dimension variations of integrated circuit features during fabrication processes. However, as the size of features on an integrated chip decrease, it becomes increasingly difficult control critical dimension variations of integrated chip features.